1. Field of the Invention
Aspects of the present invention relate to an electrode for a fuel cell and a fuel cell employing the same; more particularly, to an electrode for a fuel cell in which materials having an affinity for phosphoric acid are evenly dispersed within the electrode to ensure that phosphoric acids preferentially penetrate into micropores and thus prevent cell performance deterioration caused by the presence of excess phosphoric acid in the electrode; and a fuel cell whose efficiency is improved by employing the electrode.
2. Description of the Related Art
Fuel cells using a polymer electrolyte membrane as an electrolyte are expected to be used as a power supply for electric cars or a distributed power generation system for domestic use since the operating temperature thereof is relatively low and miniaturization is possible. Polymer electrolyte membranes used in polymer electrolyte membrane fuel cells include perfluorocarbonsulfonate polymer membranes, for example, NAFION® (DuPont Company).
However, this type of polymer electrolyte membrane needs moisture to show proton conduction, so humidification of the membrane is needed. Further, hot operation at a temperature of 100° C. or higher is required to increase the cell system efficiency sufficiently; however such a high temperature evaporates and dries up moisture in an electrolyte membrane, thereby resulting in dysfunction as a solid electrolyte.
To solve such problems originating from the conventional techniques, an unhumidified electrolyte membrane which can operate at high temperatures in excess of 100° C. has been developed. For example, Japanese Patent Laid-open No. hei11-503262 discloses materials for composing unhumidified electrolyte membranes, including polybenzimidazole doped with phosphoric acid.
Also, in low-temperature operating cells using perfluorocarbon sulfonic polymer membranes, an anhydrous electrode made by mixing polytetrafluoroethylene (PTFE), which is a water repellant, is largely used to prevent poor gas diffusion caused by ambient water or water produced during power generation at the electrodes, in particular a cathode. (An example is Japanese Patent Laid-open No. hei05-283082).
Also, in phosphoric acid-type fuel cells which are operated at temperatures of 150 to 200° C., liquid phosphoric acid is used as an electrolyte, but this liquid phosphoric acid exists within electrodes in large amounts and also inhibits gas diffusion. Thus, polytetrafluoroethylene (PTFE) is mixed within an electrode catalyst, and an electrode catalyst layer is used to prevent micropores in the electrodes from being blocked with phosphoric acid.
Also, regarding fuel cells using polybenzimidazole (PBI) containing phosphoric acid in electrolyte membranes, which combination comprises a high-temperature unhumidified electrolyte, impregnation of liquid phosphoric acid into electrodes has been attempted to improve the interfacial contact between electrodes and membranes, and there have been efforts to increase the loading concentration of metal catalysts, but satisfactory properties could not be obtained.